(1) Field of the Invention
This invention relates to a flux-cored wire electrode suitable for use in gas-shielded arc-welding, and more specifically to a flux-cored wire electrode which permits one to reduce the emission of welding fume to the same level as solid wire electrodes and is particularly suited to weld soft steel and high tensile steel.
(2) Description of the Prior Art
The use of flux-cored wire electrodes has been increasing for gas-shielded arc-welding work, because flux-cored wire electrodes have such advantages that they assure easy and efficient welding work and, especially, they feature good arc stability, produce less spatter and hence give excellent bead appearance. However, their most serious problem is that they are accompanied by a great deal of emission of welding fume. The emission of such welding fume may reach as much as 1.5-2.0 times the welding fume generally emitted when a solid wire electrode is used. Emission of a large volume of fume causes a problem from the viewpoint of labor hygiene for welding workers. Besides, it becomes difficult to see the weld line due to fume when welding in a poorly-ventilated room, thereby raising another problem that the accuracy of the welding is lowered.
As methods for solving such problems, it has been contemplated to practice such countermeasures as (1) reduction of the fume concentration by ventilation; (2) suction and discharge of fume through a duct or the like provided near the site of welding work; (3) wearing of dust mask; and (4) reduction of fume through improvements to welding materials and method. Regarding the countermeasures (1) through (3) out of the above-referred to countermeasures, a variety of methods and apparatus has already been proposed. These proposals are however posterior measures and cannot be considered as any break-through and perfect countermeasures. It should be considered as the most important countermeasure against fume to lower the emission of fume, as indicated as the countermeasure (4) above. No sufficient investigations have however been made on this point.
With the foregoing in view, the present inventors have carried out research with a view toward achieving the lowering of fume emission of flux-cored wire electrodes, which are suitable for use in gas-shielded arc-welding, from the aspect of materials making them up. As a result, it has already found that the emission of fume can be reduced to a considerable extent when the carbon content in the covering soft steel making up a sheath and the carbon content in a residual lubricant adhered in the forming step of the flux-cored wire electrode are lowered as much as possible. In the course of proceeding with the research further, it has also been found that the emission of fume can be lowered further when the composition of the filled flux is suitably adjusted in addition to the above-mentioned reduction in the carbon contents, leading to completion of this invention.